An engine operating under varying engine load and speed conditions may be improved by varying engine compression ratio. For example, during low engine loads, the engine compression ratio may be increased to improve engine efficiency. During high engine loads, the compression ratio may be decreased to threshold levels that minimize occurrence of engine knock due to high temperature and pressure in combustion chambers in the engine. In this way, the engine may be adjusted to produce a variable compression ratio based on engine load, speed and other factors. By varying the compression ratio based on engine operating conditions, engine overall performance and efficiency may be improved.
Numerous approaches of adjusting the compression ratio in the engine may include altering geometry of the combustion chamber and modifying other engine accessories. One example approach is shown by Ma in U.S. Pat. No. 5,101,776. Therein, a variable compression ratio engine includes a combustion chamber connected to an auxiliary chamber via a flow passage having a poppet valve. In order to achieve low engine compression ratios, the poppet valve may be opened to allow flow of charge gas from the combustion chamber into the auxiliary chamber. Alternatively, high compression ratios in the engine may be realized by closing the poppet valve to isolate the auxiliary chamber from the main combustion chamber.
However, the inventors herein have recognized potential issues with such a system. For example, the energy contained in the charge gas bled from the main combustion chamber into the auxiliary chamber may not be adequately recovered during engine operation. Further, substantial modification to geometry of the combustion chamber, which may introduce additional manufacturing and assembly complexity, is required in the above design of the variable compression ratio engine.
In one example, the issues described above may be addressed by engine system may comprise: varying a compression ratio of a cylinder by selectively releasing combustion charge from a cylinder to a manifold via a bleed valve on a cylinder head; and transforming the released combustion charge into usable electrical power at a turbine generator coupled downstream of the bleed valve. The manifold may be configured with an internal passage that diverts combustion charge gas from the cylinder into the turbine generator when both the bleed and check valves are adjusted to open valve positions.
By adjusting the flow of combustion charge gas from the cylinder into the manifold, engine compression ratio may be varied based on engine operating conditions while producing electrical energy from the charge gas bled from one or more cylinders. In this way, the engine compression ratio may be varied without altering geometry of any of the cylinders and while promoting better engine performance under a wide range of engine speeds and loads.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.